Project Corvette Z06: Replacing the Clutch

Autocross can be tough on clutches, since every run requires launching the car from a dead stop. We noticed the clutch slipping on our 98,000-mile C5 Corvette Z06 during the last event, which meant it was time for an upgrade. That’s easier said than done: Corvettes have transaxles in the back instead of traditional transmissions behind the engine, meaning a clutch replacement is quite complicated. To change the clutch, most of the driveline has to come out of the car, along with the rear suspension cradle. It would be a shame to disassemble the car that far without taking care of a few “while we’re in there” jobs, and just like that our simple clutch replacement had creeped into a full-on maintenance odyssey for our poor Corvette.

We’ve never split a Corvette in half before, so we enlisted the help of a few experts: The Vette Doctor in Melbourne, Florida is full of GM factory-trained technicians. They work on every generation of Corvette every day of the week (hard to find more of an expert than that). They were kind enough to walk us through their process, and point out a lot of the potential hazards and service possibilities along the way.

For example, once you remove the transmission and torque tube, it’s going to be your best opportunity to replace the drive couplers and bearing in that torque tube. Should they fail later, it means another major disassembly. Ditto with the leak-prone rear engine cover plate and rear axle seals. A little bit of preventative maintenance while the car is apart may sting the wallet a bit, but not as bad as having to do it all again should there be a preventable failure once it’s back together.

What did we put back into our Corvette? We chose the Quarter Master Optimum-SR single-disc clutch and flywheel combination. Our stock clutch disc, pressure plate and flywheel assembly weighed in just a hair over 49 lbs. Our Quarter Master setup weighs in a little below 39 lbs, dropping just over 20% of the rotating mass of the assembly. It reduces enough rotating mass to help the engine rev a bit quicker, but not so much that it becomes intractable at part throttle or off-idle. It’s an excellent compromise, especially considering we increased clamping force as well–the new clutch can handle up to 700 horsepower and 500 ft.-lbs. of torque. Since this is primarily an autocross and track car, precise launches and shifts are critical. We also wanted some additional clamping force and friction, since we’re planning on adding power in the future. Why didn’t we choose some 8-disc wonder clutch that can hold 1500 ft.-lbs.? We didn’t want to sacrifice street manners for capability we’d never really need.

The crew at The Vette Doctor was kind enough to share some of their driveline maintenance tips with us on an edition of Grassroots Motorsports LIVE! Check out that episode below:

Did you go into the diff while you were there? The Belleville washers that place a preload on the plates are known to break. While you are there replace them and install a fresh set of plates as well.

We didn't but that's on our list for the next few months. We're currently researching various diff rebuild strategies (stock vs upgraded stock vs aftermarket diff, etc.) and seeing what makes the most sense.

So I was balls deep in this exact project a few years ago and learnt a few things. Whether or not this is A/X legal I have no idea, it was for a hot street car that saw occasional drag strip time.

Definitely re-seal the rear diff while its apart, new O-rings and new axle seals, can be done in chassis but not as easy as when its out.

You can take just the rear diff off the trans pretty easily in chassis - drop the lower subframe, angle the torque tube, and it (just barely) sneaks out. Its not easy to pull the trans off the torque tube in chassis, as a matter of fact it may be impossible. I always pulled the torque tube.

I replaced the bearings in the torque tube with new Timkens and installed the upgraded poly couplers from Driveshaft Shop while my torque tube was out. There is a little snap ring behind the dust shield on one of the bearings of the torque tube that is well hidden. Eventually you will find it with a 50 ton press and then you will need a new snap ring.

Some guys like solid couplers or one solid one OEM coupler but that is noisier than 2 upgraded DSS couplers.

Some guys use BMW Lobro joints in place of the OEM couplers, they are softer and I wouldnt recommend.

Prothane 6 shooter couplers are garbage and do not hold up.

The Z06 has shot peened gears but the diff is otherwise identical to other cars. If you are changing the gears it does not matter which pumpkin you start with as long as it is 3.42 ratio, the carrier on the numerically lower ratios are different. You can get a spacer and longer bolts if you want to use a cheaper carrier. All the carrier castings are the same so you can mix n match guts as long as you have a shim kit to check setup.

Setting up the gears requires a factory J tool set. Anyone who does it any other way is either a liar or getting lucky.

Replace the belleville washers and frictions in the diff with C6 Z06 parts.

Replace the one piece halfshaft and thin longer halfshaft with C6 Z06 parts.

Replace the pinion support with the C6 Z06 pinion support

Get a Pfadt diff brace (are these still available? Did someone else start making them? I had an OG Pfadt before they screwed everyone and took their money)

Get a ECS trans brace.

ECS trans brace and Pfadt diff brace and coilovers completely eliminated my wheel hop on Nitto NT555Rs with a SPEC twin disc clutch. Could just rev and dump with no worries. Before that I was putting a lot of money into my driveline

If you want to be real fancy you can update a C5 to C6 Z06 trans specs, requires most of the driveline and the rear cradle. Its a way better setup. I almost pulled the trigger on that setup before deciding to rebuild and brace my stock stuff and had no problems after that.

Any more questions just ask! I have been through the C5 driveline so many times - and did it all on my back in a 2 car garage with regular man's hand tools.

I just did this job about a month ago. I didn't want to do it on my shop floor - and glad I didn't, but was fortunate that my buddy not only let me use his hoist but he actually did most of the work.

I had a rattly noise on idle, which I thought might be one of the couplings, and a noisy wheel bearing. When we pulled it apart the couplings were like new. The rear bearing in the torque tube housing was dry and you could feel (and hear) it when you ran the shaft around. That was my wheel bearing noise and it also explained why I couldn't locate it to either side. The rattling turned out to be the hub in the clutch. For some reason it was loose, though I don't suspect abuse because the part number was still legible on the friction material and everything else looked super clean. We didn't expect to find that and were under the gun time wise so I got what was the right combination of price and availability and upgraded to the LS7 CL/PP/FW.

All in all it was not a bad job. The car is very well put together and very easy to work on.

Oh yeah one more thing if you wheel hop you WILL break stuff! I killed two axles, both driveline couplers, two transmissions and three differentials before I went all in on it. Cryo/shot peen everything, brace it to the moon, coilovers and tire pressure helped a ton! In hindsight I wanted a tire that was somewhat streetable so I went with the Nitto NT555R Drag Radial in a 305/something-18 size and I should have gone with some taller and skinnier Quicktime Pros on 17s and said to hell with streetability on drag tires. The Quicktime Pros I borrowed wrinkled a lot better and hooked smoother on on a manual trans car. Auto cars can get away with a stiffer sidewall drag tire since you can load up the driveline and keep from blowing the tires off at the line easier.

Also these were the BITD days of living in a paid off house and no marriage/SWMBO keeping my spending in check. I dont think I would want to dump that sort of money into a car any more.